Cold cathode tube



6, 1940- w. Rosowsm I I 2,210,127

COLD CATHODE TUBE Filed Dec. 7, 1935 IIIIIIIIIIIIflIl/III Regan skiPatented Aug. 6, 1940 UNITE STATES 2,210,127 001.1) GATHODE TUBEApplication December 7, 1935, Serial No. 53,355

6 Claims.

In the operation of cold cathode. tubes such as the electron or iontubes employed in oscillographic and television or picture transmittingarrangements or in X-ray devices, for example, it is well known todeflect the electrons with respect to an annular diaphragm in order tovary the intensity of the cathode ray. In this way however not only thecurrent density of the ray on the oposite side of the diaphragm but alsothe shape of the spot on the receiving screen is varied, this shapechanging from a circular form to a crescentic one in the best possiblecase, if not as an additional result the spot is displaced. No othermethods of varying the intensity of a ray of electrons have beenproposed with regard to cold cathode tubes. In particular it has notbeen attempted in the case of cold cathode ray oscillographs ortelevision tubes, for instance, to vary the intensity of the ray ofelectrons by varying the current density of the ray without altering thespot shape, as has been known with glowing cathode oscillographs for along time.

The invention described hereafter shall enable such variations ofintensity to be effected also in the case of cold cathode tubes. This isin accordance with the invention attained by varying the quantity ofelectrons conveyed to the space intended for deflecting the ray ofelectrons, such variation being accomplished by means of rota-' out inthe appended claims, reference being had to the accompanying drawing inwhich Figs. 1

40b to 7 are diagrammatic sectional views each showing an embodiment ofthe invention. Similar parts are denoted by the same reference numerals.

The simplest means of effecting the invention.

452 consists in making the cathode hollow so that it forms a sort ofFaraday cage of a certain depth, and to dispose control electrodes inthis cage which are of a rotation-Symmetrical construction. Theseelectrodes must have sufilciently 50.;large openings for the ions orelectrons to pass.

through. Arrangements of this kind are shown in Figs. 1 to 3.

In the arrangement according to Fig. l the cathode I has a hollow 3 andtowards the anode 55 2. .an opening 4. K denotes the cathode ray. By

M, I! two continuous voltage sources are designated. This arrangementmay belong to a cold cathode ray oscillograph. The ions in consequenceof the long free path they have to pass through, readily pass throughthe opening 4, as has been shown by the well known canal rayexperiments. At the spot 5 where they hit against the inner surface ofthecathode, electrons are released. The, initial velocity of theelectrons is low at first and in the hollow 3 remains low because theopening 4 isso narrow that the field of the anode 2 can only to a smallextent penetrate through this opening. In consequence thereof arotation-symmetrical control electrode 6 can by means of a comparativelysmall poten tial either drive back or extract the electrons released. at5, this depending on the polarity of the electrode, so that with the aidof such electrode'an intensity regulation of the useful ray of electronsispossible without the spot-shape. undergoing any change. Since the ionsalways have a comparatively high velocity they are not influenced by thesmall control voltages in a manner worth mentioning. The control fieldsare preferably electrostatic but may be also of the magnetic type.

It is desirable that the electrons arising at 5 be given a certain lowvelocity at first in order that the ray of electrons have an appropriateshape, that is to say, have not too large a top angle. To such endit isappropriate to employ not only a single control electrode but a numberthereof and in such a' manner that the electrons are in the first placegiven velocity and ray shape and that only after this they are givenintensity fluctuations by' means of a negative electrodeor electrodes ofa variable potential. InFig. 2-the numeral 1 indicates the suctionelectrode, connectedto the positive pole of a voltage source l9, While 6again denotes the control electrode.

It may be advantageous to arrange the electrode 6 to. form a wall of theFaraday cage or cathode 4. Such an arrangement is shown in Fig. 3. I I

As represented in Fig.4, the cathode I may in the usual manner be planeor curved without being hollow. In such, case it is only necessary. todispose the control electrodes in a sufficiently close proximity to thecathode l in order that low control voltages shall be-sufficient.

Furthermore, with a cold cathode of the type shownin Fig 4 the cathoderay may be so shaped as to be given a certain low velocity over acertainpart of its length and to be readily controllable therefore. Tosuch end the electrons produced in a normal manner must pass through arotation-symmetrical counter field. 'As is well known such an actionalso entails a concentration of the electrons. If then the electrons,concentrated and retarded in this way, pass through arotation-symmetrical control electrode, they can here be modified intheir intensity, as stated before, by means of a comparatively lowvoltage. Arrangements of this kind are illustrated in Figs. 5 and 6. Thearrangement according to Fig. 5 is purely schematic whilst Fig. 6 in adiagrammatic representation shows a device adapted for practicalpurposes.

Either of these two arrangements has an electrode 8 that serves toproduce the said rotationsymmetric counter field, and is provided alsowith annular diaphragms 9 between which the control electrodes 6 arelocated to which the variable control potential is conducted. Thediaphragms 9 serve for limiting the control range. After the intensityregulation of the ray of electrons by means of the electrodes 6, theelectrons may again be accelerated in a known manner The diaphragms 9shown in Fig. 6 are arranged to form a Faraday cage.

The diaphragms 9 must have a somewhat higher potential than has thecathode I in order to allow the electrons originating from this cathodeto pass through. The electrodes H], II are preferably connected to thesame potential as the anode 2.

The arrangements described heretofore have still certain disadvantageswhich may sometimes be troublesome, which however are easy to overcomeby means of the further invention.

In a number of practically important cases not only a variation. of thequantity of electrons but also a variation of the output requires to betaken into consideration, that is to say a variation of the product ofthe number of electrons and the velocity. of these. Such is the case forinstance with television systems, the fluorescent screen mainlyresponding to this output, and is the case also with X-ray tubes. Incases of this kind the novel method of regulating the quantity ofelectrons can only be successful if the voltage source which is tosupply the cathode-anode voltage is of such characteristic that with avariable number of electrons a sufficiently constant cathode-anodepotential is produced. There are however voltage sources which when hereemployed tend to decrease the anode-cathode potential whenever thequantity of electrons is increasing, and to decrease this potential tosuch an extent that any effectual change in the said output will notoccur. This drawback can be overcome, at least to a considerable extent,by connecting the tube to a voltage source that within certain limitswith increasing load does not show a considerable drop of potential. Inthis case a resistance I3 (Fig. 7) must be interposed in the circuitcomprising the anode and cathode, because otherwise the weak dischargeof the tube may happen to turn into a strong discharge so as to destroythe tube (falling characteristic); butit will in general be possible toso dimension this smoothing resistance that although not the number ofelectrons but the said output is more or less impaired in its ability ofbeing controlled, yet the result of controlling the output will besuitable for practical purposes.

In accordance with the further invention the output control may beimproved considerably by interposing the resistance I3 between the anode2 and the voltage source l4. Appropriately, the anode is provided with anarrow opening l5 which the ray of electrons is caused to pass through.In order to perform this, means for concentrating the ray may be used,such as the electrodes 8 shown in Figs. 5 and 6. After the anode asecond annular diaphragm I6, likewise of a rotation-symmetricalconstruction, is disposed according to the invention. This diaphragm I6is in direct connection with the positive pole of the voltage source l4so that between cathode l and diaphragm Hi the entire voltage is active,whereas the voltage active between cathode l and anode 2 is smaller bythe drop of potential due to resistance l3. On varying the quantity ofelectrons the potential difference which there is between anode 2 anddiaphragm l6 acts to impart an additional velocity to the electrons sothat on the receiving plate l8 not only the quantity of electrons butalso the electronic output and thus the brightness is controlled to afull extent. The advantage of the arrangement is that the resistance l3will pre-. vent the discharge between cathode and anode from turninginto a discharge richer in current.

On the other hand however a discharge rich in current can likewise notarise between cathode l and diaphragm 16 because the narrow anode borel5 forms a large resistance to thegas discharge,

The fundamental idea of the last described arrangement is that despitethe fact that the quantity of electrons is variable and that further theanode-cathode voltage cannot be prevented from undergoing variations, anadditional field is created by means of a second diaphragm I6, thisfield acting to compensate the. variation to which the anode-cathodepotential is subjected.

- There are still other possibilities to carry this idea into effect.For example, the drop of potential due to resistance I3 may be used forcon-- trolling .an electron tube which in its turn leads' a suitablychosen voltage to the cold cathode tube by variation of the anodecurrent, so as to care for a suitable potential difference between anode2 and diaphragm I6. The arrangement represented in Fig. 6 however is thesimpler means for neutralizing the drop of potential due to resist ancel3.

As long as the anode-cathode discharge is purely self-acting thedescribed" means are not adapted to afford a large range of regulationor control. This is attributable to the fact that if the quantity ofelectrons is decreased by such regulation the conditions for theexistence of a stable gas discharge are growing more and moreunfavourable, so that finally the discharge is interrupted. As is wellknown all self-acting gas discharges have the property of being suddenlyextinguished with av sufiiciently small current. The use of, smallercurrents in this connection requires a very high voltage and very greatresistances in series connection to be employed, whereby however theoutput regulation or control is rendered extremely difiicult, as will beunderstood from the previous statements. But even then it will be seenthat with a lower limit the discharge must stop, so that a new ignitionmust be brought about, the ignition voltages being in general muchhigher than the voltages of operalation effected within wide limits,such as deemed necessary for instance in the case of television, picturetransmission, X-ray purposes, etc.

It is well known however to operate cold cathode tubes by means of anauxiliary discharge. The further invention therefore proposes to employsuch auxiliary discharge in combination with the novel method ofcontrolling the quantity of electrons in order to enlarge the range ofregulation in the case of cold cathode tubes. In this way the tube canbe controlled also in the case of small current intensities and thus beused for television and similar purposes, such as picture transmission,X-ray purposes, etc.

What is claimed is:

1. A cold cathode tube comprising a cathode, means including a controlelectrode for producing a rotation-symmetrical field,'saidrotation-symmetrical field being disposed in the region of low velocityof the electrons to provide intensity control, and means in theimmediate proximity of said control electrode between said electrode andsaid cathode for causing said electrons to pass through a common pointwhereby low velocity of said electrons is assured.

2. A cold cathode tube comp-rising a cathode having an emitting surfacesubstantially perpendicular to the axis of said tube and extended fromsaid surface to form a hollow cylinder, and an auxiliary controlelectrode within said cylinder producing axial-symmetrical fieldsoperating substantially along the axis of said tube for controlling theintensity of the electrons emitted from said cathode.

3. A cold cathode tube arrangement comprising, a cathode means includinga control electrode for producing a rotation-symmetrical field, saidcontrol electrode being disposed in the region of low velocity of theelectrons for the purpose of intensity control, means in immediateproximity with said control electrode for causing said electrons to passthrough a common point, a continuous voltage source adapted on variationof the current load to care for the variation of the cathode-anodevoltage being small enough to enable the electronic output to beregulated, an anode operatively associated with the said cathode, and aresistance interposed between this anode and the positive pole of saidvoltage source.

4. A cold cathode tube arrangement comprising, a cathode means includinga control electrode for producing a rotation-symmetrical field, saidcontrol electrode being disposed in the region of low velocity of theelectrons for the purpose of intensity control, means in immediateproximity with said control electrode for causing said electrons to passthrough a common point, a continuous voltage source adapted on variationof the current load tocare for the variation of the cathode-anodevoltage being small enough to enable the electronic output to beregulated, an anode operatively associated with the cathode and providedwith a bore, a resistance interposed between this anode and the positivepole ofsaid voltage source, and an annular diaphragm connected directlyto this pole.

5. A cold cathode tube arrangement comprising, a cathode means includinga control electrode for producing a rotation-symmetrical field, saidcontrol electrode being disposed in the region of low velocity of theelectrons for the purpose of intensity control, means in immediateproximity with said control electrode for causing said electrons to passthrough a common point, an anode operatively associated with saidcathode, an annular diaphragm, this anode being located between thisdiaphragm and the cathode, a continuous voltage source, a resistanceinterposed between the positive pole thereof and the anode, and meansfor causing thedrop of potential due to this resistance to generate apotential difference between said cathode and diaphragm.

6. A cold cathode tube arrangement comprising, a cathode means includinga control electrode for producing a rotation-symmetrical field,

